Add hamburger-menu recipe

[iainnicol]

• package summary: A hamburger menu button for the Emacs mode line. Use instead of
  `menu-bar-mode' to save vertical space.
• URL: https://gitlab.com/iain/hamburger-menu-mode
• submitter relationship to package: author

[purcell]

Great, thanks!

[iainnicol]

Thanks for taking the time to review my package.